Host processor systems may store and retrieve data using a storage device containing a plurality of host interface units (I/O modules), disk drives, and disk interface units (disk adapters). The host systems access the storage device through a plurality of channels provided therewith. Host systems provide data and access control information through the channels to the storage device and the storage device provides data to the host systems also through the channels. The host systems do not address the disk drives of the storage device directly, but rather, access what appears to the host systems as a plurality of logical disk units. The logical disk units may or may not correspond to any one of the actual disk drives. Allowing multiple host systems to access the single storage device unit allows the host systems to share data stored therein.
In some cases, it is desirable to replace a storage device with a new storage device without pausing or disrupting operation of a host while maintaining a disaster recovery position in which the host can resume operation if either of the storage device or the new storage device fails during the migration. A system for doing this is disclosed, for example, in U.S. Pat. No. 7,685,129 to LeCrone, et al., which teaches performing data migration without disrupting operation of the host. However, that system and similar systems use the host to read data from the storage device and write the data to the new storage device, which means that a significant amount of the data being migrated passes through the host. In some cases, this may be impractical (due to the volume of data) or at least less than optimal for a particular situation.
Accordingly, it is desirable to be able to migrate data from a storage device to a new storage device without disrupting host operations while always maintaining a disaster recovery position in a way that does not require a significant amount of data to pass through the host.